The invention relates to a secondary part of a linear electrical machine. The linear electrical machine is, in particular, a linear motor. If the linear motor is a synchronous motor, then the linear motor can also easily be used as a generator.
The linear electrical machine has a primary part and a secondary part. These machine parts can be produced with high dimensional accuracy. This relates in particular to the height dimensions of the linear electrical machine, for example the height of the external size, or else the height of an air gap between the primary part and the secondary part. Compliance with specified tolerances requires manufacturing effort, and is therefore costly. The large amount of manufacturing effort is incurred, for example, by a manufacturer of the secondary parts or else by a supplier of semi-finished goods for production of the secondary parts of the linear electrical machine.
The secondary part has a mount to which the permanent magnets are fit. This means that the permanent magnets are positioned on this permanent-magnet mount. The mount—the permanent-magnet mount—is, for example, in the form of a mounting plate which has been manufactured from an iron plate. The height of the mount is its thickness in which case, for example, the thickness may be 6 mm to 12 mm. By way of example, the thickness tolerance is ±0.2 mm or else ±0.5 mm. The tighter the tolerance, the more complex it is to produce.
The height of the secondary part therefore depends both on the height of the permanent magnets and on the height of the mount. The height of these parts in this case relates to the size on a plane on which the air gap height can also be measured between the primary part and the secondary part.
The secondary part may also have encapsulation. The encapsulation can also influence the height of the secondary part. The material of the encapsulation which is located in the area of the air gap has a thickness, for example, of about 0.4 mm. Depending on the tolerances of the mount and of the permanent magnets, the thickness of the encapsulation is normally subject to a tolerance of ±0.25 mm. The air gap width is the height of the air gap. The narrower the air gap is, the greater is the power produced by the electrical machine. If the air gap has different widths, depending on the height of the permanent magnets, this has a negative effect on the machine behavior since, in consequence, the magnetic flux is different and the achievable electromotive force (EMF) is therefore also different. A secondary part which has encapsulation is known, for example, from DE 199 36 064 A1.
A specified tolerance for the installation height of the secondary part can be ensured either by using secondary-part components which do not exceed specific tolerances or by subsequently matching the height of the secondary part by means of a reworking process. Both involve a large amount of effort. Further problems can occur, in particular if the mount is reworked. The thickness of a mount, which also governs the installation height of the secondary part, can be adjusted, for example, by means of grinding or by means of a milling process. Grinding is extremely time-consuming. In the case of a mount produced from a rolled metal sheet for permanent magnets, the milling process leads to bending since the rolling process results in internal stresses in the rolled metal sheet. This problem could admittedly be overcome, for example by an annealing process, but this requires a large amount of effort.